New electyroluminescent phenyl-subsituted polyfluorenes synthesized in supercritical carbon dioxide

Full text of DOI:10.1134/S0012500810060029

ISSN 0012ꢀ5008, Doklady Chemistry, 2010, Vol. 432, Part 2, pp. 159–164. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © M.L. Keshtov, E.I. Mal’tsev, A.M. Lopatin, L.N. Nikitin, I.A. Blagodatskikh, M.N. Buzin, S.M. Pozin, A.R. Khokhlov, 2010, published in Doklady Akaꢀ
demii Nauk, 2010, Vol. 432, No. 4, pp. 490–495.
CHEMISTRY
New Electyroluminescent PhenylꢀSubsituted Polyfluorenes
Synthesized in Supercritical Carbon Dioxide
M. L. Keshtova, E. I. Mal’tsevb, A. M. Lopatina, L. N. Nikitina, I. A. Blagodatskikha,
M. N. Buzina, S. M. Pozinb, and Academician A. R. Khokhlova
Received January 18, 2010
DOI: 10.1134/S0012500810060029
Blue luminescent polymers have attracted considꢀ of residual highꢀboiling solvents and metal catalyst
erable recent attention, both academic and practical,
due to their application in fullꢀcolor displays and
green, red, and white LEDs, as well as in design of
nextꢀgeneration light sources [1–4]. Therefore, develꢀ
opment of efficient blue luminescent polymers is of
importance for such applications.
traces. In this context, in this work, we have suggested
a new catalystꢀfree method of synthesis of highꢀpurity
electroluminescent polymers based on phenylꢀsubstiꢀ
tuted polyfluorenes (PSPFs) in supercritical carbon
dioxide. The PSPF synthesis by the Diels–Alder reacꢀ
tion in supercritical carbon dioxide afforded highꢀ
purity polymers free of traces of highꢀboiling solvents
and metal catalysts. The presence of a large number of
side bulky phenyl substituents made it possible to supꢀ
press chain aggregation and improve the solubility and
filmꢀforming properties [6, 7].
Among blue electroluminescent polymers, of most
interest are polyfluorenes (PFs) and their derivatives,
which exhibit high quantum luminescence yields and
excellent chemical and thermal stability and photostaꢀ
bility [5]. However, they are not free of disadvantages.
Alkylꢀsubstituted PFs exhibit poor electroluminesꢀ
cence and low color stability due to polymer chain
Bis(triarylcyclopentadienone), a key monomer for
aggregation, oxidative destruction, and the presence PSPF synthesis, was obtained by Scheme 1.
4
1
5
3
6
Br
C H Br
2
8
17
Br
Br
Br
Br
7
2
C8H17
C8H17
9
8
I
II
2
II
Pd
C8H17
C8H17
III
a Nesmeyanov Institute of Organoelement Chemistry,
Russian Academy of Sciences, ul. Vavilova 28, Moscow, 119991 Russia
b Frumkin Institute of Physical Chemistry, Russian Academy of Sciences,
Leninskii pr. 31, Moscow, 119991 Russia
159

160
KESHTOV et al.
KMnO4
III
O O C8H17
C8H17 O O
IV
O
2
2'
O
7
2
1'
IV
3'
9
O
5'
C8H17
C8H17
4'
V
Scheme 1.
At the first stage, fluorine was brominated to give the elemental analysis data corresponded to the calcuꢀ
compound I, which was then introduced into the reacꢀ
tion with a twofold molar amount of bromooctane.
Then, the resulting 2,7ꢀdibromoꢀ9,9ꢀdioctylfluorene
lated values. The structures of these compounds were
confirmed by IR and 1H and 13C NMR spectra (Table 2).
The 1H NMR spectra of bis(cyclopentadienone)
are rather complicated. The aromatic protons give rise
to downfield multiplets in the range 6.80–7.53 ppm
V
(
II) was crossꢀcoupled with a twofold molar amount of
phenylacetylene in the presence of a Pd catalyst.
2,7ꢀBis(phenylethynyl)ꢀ9,9ꢀdioctylfluorene (III) thus
obtained was oxidized by potassium permanganate
to 2,7ꢀbis(phenylglyoxalyl)ꢀ9,9ꢀdioctylfluorene (IV),
which was treated with 1,3ꢀdiphenylacetone to proꢀ
δ
(m, 36H), and the signals of the aliphatic protons are
observed in the high field in the range 0.25–1.50 ppm
(m, 34H). However, the integrated intensity ratio of
the aromatic and aliphatic parts corresponds to the
suggested structure. In this case, the 13C NMR spectra
duce the target monomer (
thesis (Scheme 1) and study of compounds
summarized in Table 1. As is seen, the intermediate
and target products were obtained in high yields and shows downfield signals near 200 ppm typical of the
V
). Some results of this synꢀ
I–V
are
are more informative. The spectrum of compound
V
Table 1. Characteristics of compounds I–VII
Elemental analysis (found/calculated), %
Compound
Yield, %
Tm
,
°
C
Empirical formula
C
H
Br
48.40
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ
2.22
ꢀꢀꢀꢀꢀꢀꢀ
49.53
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ
I
93.2
91.2
85.2
96.8
95.4
94.05
82.2
161–163
52–54
C13H8Br2
C29H40Br2
C45H50
48.19
2.49
49.32
63.10
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ
7.39
ꢀꢀꢀꢀꢀꢀꢀ
29.09
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ
II
63.51
7.35
29.14
90.55
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ
9.21
ꢀꢀꢀꢀꢀꢀꢀ
III
IV
V
82–84
–
91.47
8.53
81.24
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ
7.35
ꢀꢀꢀꢀꢀꢀꢀ
91–93
C45H50O4
C75H70O2
C39H58Si2
C33H42
–
–
–
–
82.53
7.70
90.10
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ
7.10
ꢀꢀꢀꢀꢀꢀꢀ
168–170
89–91
89.77
7.03
81.13
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ
10.71
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ
VI
VII
80.34
10.03
90.21
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ
7.94
ꢀꢀꢀꢀꢀꢀꢀ
44–46
90.35
9.65
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NEW ELECTYROLUMINESCENT PHENYLꢀSUBSITUTED POLYFLUORENES
161
carbonyl group of the cyclopentadienone moiety, and potassium carbonate. The structure of compound VII
was confirmed by 1H and 13C NMR and IR spectrosꢀ
copy. The 1H NMR spectrum shows two doublets and
two singlets at 7.62, 7.47, 7.45, and 3.14 ppm due to
the aromatic and terminal ethynyl protons of the fluoꢀ
rene fragment, respectively. The13C NMR spectrum of
compound VII shows two signals at 85.50 and
76.98 ppm characteristic of the acetylene moiety. The
IR spectrum shows a band at 2107 cm–1 characteristic
the number of characteristic signals in the aromatic
and aliphatic ranges 169–110 and 13–60 ppm, respecꢀ
tively, corresponds to the suggested structure. The
structure was also proved by IR spectra. In particular,
the IR spectrum of compound
V shows a band at
1711 cm–1 corresponding to stretching vibrations of
the carbonyl group.
To obtain PSPFs, we used the simplest bis(acetylꢀ
ene)s pꢀdiethynylbenzene and 4,4ꢀdiethynyltolane, as
well as 2,7ꢀdiethynylꢀ9,9ꢀdioctylfluorene (VIIa), synꢀ
thesized by Scheme 2.
of the
C
≡
C bond.
PSPFs VIIIa–VIIIc were synthesized by the reacꢀ
tion of equimolar amounts of bis(cyclopentadienone)
Si
V
with bis(ethynyl)s VIIa VIIc in supercritical carbon
–
II
Si
Si
Pd
dioxide according to Scheme 3. PSPFs were syntheꢀ
sized in supercritical carbon dioxide at 200 bar and
180 С for 10 h. The structure of the polymers was conꢀ
firmed by IR spectroscopy and H and C NMR.
Their IR spectra lack the signals typical of the C=O
(1711 cm–1) and
C8H17
C8H17
VI
°
1
13
KOH
VI
C C
(2107 cm–1) groups of the cyꢀ
≡
C8H17
C8H17
VIIa
clopentadienone and ethynyl moieties, respectively.
For all polymers, the C NMR signals near 200 and
13
Scheme 2.
80 ppm typical of the cyclopentadienone and ethynyl
13
1
moieties are absent in the C NMR spectra. The H
NMR spectra are rather complicated; however, the inꢀ
tegrated intensity ratio of the aromatic and aliphatic
signals is consistent with the suggested structures (see
2,7ꢀDiethynylꢀ9,9ꢀdioctylfluorene (VII) was synꢀ
thesized by Pdꢀcatalyzed crossꢀcoupling of 2,7ꢀ
dibromoꢀ9,9ꢀdioctylfluorene with a twofold molar
amount of trimethylsilylacetylene with the subsequent
removal of the trimethylsilyl group by treatment with Experimental).
Table 2. Spectral characteristics of compounds I–VII
NMR; δ, ppm (CDCl3)
Comꢀ
pound
IR;
ν
, cm–1
1H
13C
I
–
–
7.62 (s, 2H), 7.58 (d, 2H), 7.48 (d, 2H), 3.83 (d, 2H) 151.26, 137.86, 129.23, 126.10, 120.98, 120.00
7.53 (d, 2H), 7.46 (d, 2H), 7.44 (d, 2H), 1.91 (m, 4H), 152.44, 138.94, 130.04, 126.07, 121.38, 120.96,
II
1.26–1.05 (m, 20H), 0.83 (t, 6H), 0.58 (m, 4H)
55.56, 40.03, 31.63, 29.78, 29.04, 29.01, 23.53,
22.47, 13.94
III
IV
V
C
≡
C
7.34–7.66 (m, 16H), 0.5 (4H, CH2), 0.71–0.78
151.0, 140.6, 131.60, 130.71, 128.32, 128.21,
125.92, 123.34, 121.92, 119.90, 90.31, 89.73,
55.21, 40.42, 31.51, 29.73, 23.72, 22.61, 13.92
2095 (m, 6H, CH3), 0.9–1.1 (m, 20, CH2), 1.95–2.05
3243 (m, 4H, CCH2)
C=O 7.50–8.05 (m, 16H), 0.5 (4H, CH2), 0.71–0.78 194.40, 193.80, 151.26, 145.51, 135.62, 134.91,
1664 (m, 6H, CH3), 0.9–1.10 (m, 20H, CH2), 1.95–2.05 133.22, 130.63, 129.01, 127.11, 123.32, 120.4, 55.91,
(m, 4H, CCH2)
40.72, 32.34, 30.87, 29.77, 29.52, 24.10, 22.91, 14.58
C=O 6.80–7.53 (m, 36H, Ar), 0.25 (m, 4H, CH2),
1711 0.82–0.91 (m, 6H, CH3), 0.95–1.25 (m, 20H, CH2), 132.56, 130.97, 130.81, 130.19, 129.36, 128.50,
200.24, 155.23, 154.23, 150.74, 141.00, 133.25,
1.42–1.50 (m, 4H, CCH2)
128.43, 128.09, 128.05, 127.81, 127.53, 127.43,
125.49, 125.30, 123.71, 119.75, 55.05, 40.23,
31.99, 30.03, 29.68, 29.49, 23.73, 22.72, 14.19
VI
C
≡
C
7.58 (d, 2H), 7.44 (d, 2H), 7.41 (s, 2H), 1.92 (m, 4H), 150.91, 140.83, 131.20, 126.19, 121.76, 119.79,
2149 1.21–1. 0.1 (m, 20H), 0.83 (m, 6H), 0.53 (m, 4H), 106.07, 94.21, 55.21, 40.30, 31.75–22.56 (CH2),
0.18 (s, 18H, SiMe3) 14.04 (CH3), 0.17 (SiMe3)
VII
C≡
2107 3.14 (s, 2H, C C), 0.80–1.95 (m, 34H, al) 76.98, 55.18, 40.17, 31.73–22.54 (CH), 14.02 (CH3)
C
7.62 (д, 2H, Ar), 7.47 (d, 2H, Ar), 7.45 (s, 2H, Ar), 150.92, 140.87, 131.13, 126.42, 120.70, 119.87, 84.50,
≡
DOKLADY CHEMISTRY Vol. 432
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162
KESHTOV et al.
V +
Ar
VIIa–VIIc
Ar
C8H17
C8H17
n
VIIIa–VIIIc
Ar =
(a),
(b),
(c)
.
C8H17
C8H17
Scheme 3.
The weightꢀaverage and numberꢀaverage molecuꢀ action in the system. In addition, of special interest is
the electroluminescent properties of all three polymer
lar weights (Mw and
Mn ) and polydispersity (Mw /Mn )
structures since organic LEDs with a broad visible
emission band are intensively studied with the aim of
using them in design of nextꢀgeneration light sources.
of the polymers determined by gel permeation chroꢀ
matography vary within the ranges 5700–11300,
30000–51500, and 3.49–5.26, respectively. All polyꢀ
mers are readily soluble in common organic solvents,
s u c h a s D M F, T H F, NꢀMP, toluene, and chloroform.
EXPERIMENTAL
The thermal and thermooxidative stabilities were estiꢀ
mated by means of DSC and TGA. The stability temꢀ
peratures of the polymers are rather high and fall
1
13
The H and C NMR spectra of the compounds
and polymers were recorded on a Bruker AMXꢀ400
spectrometer at a working frequency of 400.13 and
100.62 MHz, respectively. The IR spectra were
recorded on a PerkinꢀElmer 1720ꢀX FTIR spectroꢀ
photometer. TGA and DSC were performed on Perꢀ
kinꢀElmer TGAꢀ7 and DSCꢀ7 instruments, respecꢀ
tively, at a heating rate of 10 K/min. Electronic
absorption spectra were recorded on a PCꢀ200 specꢀ
trophotometer and the fluorescence spectra, on a
Hitachi 850 spectrofluorimeter.
within 174–253 С. The exception is polymer VIIIа,
°
which is presumably due to the large number of alkyl
groups per polymer unit. As follows from Table 3, all
PSPFs are highly thermostable. The temperature of
10% weight loss in air and argon is within 350–375 and
400–420 C, respectively.
°
The figure shows the absorption photoluminesꢀ
cence spectra of the polymers in chloroform. All three
luminescence spectra are broad bands, with the longꢀ
wavelength edge being shifted into the visible region.
According to preliminary data, the observed bands are
due to various optical transitions. The nature of each
Synthesis of Initial Compounds
2,7ꢀDibromofluorene (I). A solution of bromine
of these bands will be addressed in future studies. (62.6 g, 392 mmol) in chloroform (40 mL) was introꢀ
However, we can assume that the longꢀwavelength duced dropwise over a period of 3 min into a suspenꢀ
band is most likely caused by interchain exciplex interꢀ sion of fluorene (30 g, 182 mmol) and iron powder
Table 3. Some characteristics of polymers VIIIa
ηred, dL/g
(DMF, 25°C)
–
VIIIc
T
10% (25
°
C)
argon
Mn × 103
Mw
×
103
Mw /Mn
Tст (25°C)
Polymer
air
VIIIa
VIIIb
VIIIc
0.41
0.35
0.39
11.30
5.70
39.40
30.00
51.50
3.49
5.26
4.69
174
234
253
375
360
350
400
420
410
10.50
DOKLADY CHEMISTRY Vol. 432
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NEW ELECTYROLUMINESCENT PHENYLꢀSUBSITUTED POLYFLUORENES
163
1.00
1000
0.75
750
1
0.50
0.25
0
500
2
250
0
3
300
350
400
λ
450
500
550
, nm
–4
Absorption and fluorescence spectra of polymers (
tation with 350 nm).
1)
VIIIa, (2)
VIIIb, and (
3)
VIIIc in chloroform (
c
= 12.5 × 10 mol/L, exciꢀ
λ
(0.160 g, 2.86 mmol) in 200 mL of chloroform prelimꢀ manganate (11.56 g, 73.15 mmol), 14.17 mL of water,
inarily cooled to , while the temperature was not 5.3 mL of acetic acid, and 350 mL of acetone were
allowed to raise above . Then the mixture was placed in a threeꢀneck flask (500 mL) equipped with a
0 С
°
5 C
°
allowed to warm up to room temperature, and the stirrer, a reflux condenser, and a thermometer. The
reaction was carried out for 2 h. The resulting precipiꢀ mixture was refluxed for 2.5 h. The reaction is accomꢀ
tate was filtered off and recrystallized from chloroꢀ panied by the deposition of black MnO2. When the
form. The yield of
(93.2%).
2,7ꢀDibromoꢀ9,9ꢀdioctylfluorene (II). 1ꢀBroꢀ
mooctane (37.2 g, 194 mmol) was added to a suspenꢀ
I
with mp 161–163 С was 54.5 g
°
reaction was complete, the precipitate was filtered off
and washed two times with hot acetone. Then, the filꢀ
trate was removed on a rotary evaporator. The residue
was washed with distilled water to neutral pH, dried,
and crystallized from heptane. The yield of bright yelꢀ
sion of compound I (30.0 g, 92 mmol), benzotriethyꢀ
low crystals of IV (mp 91–93 С) was 10.76 g (96.8%).
°
lammonium chloride (0.18 g, 0.78 mmol), and sodium
hydroxide (30 mL, 50 wt %) in 400 mL of DMSO. The
reaction mixture was vigorously stirred at room temꢀ
perature for 3 h. Then, it was extracted with diethyl
ether, and the extract was washed with a saturated
sodium chloride and dried by anhydrous magnesium
sulfate. The solvent was evaporated. The residue was
recrystallized from heptane. The yield of white crystals
2,7ꢀBis(2',4',5'ꢀtriphenylcyclopentadienonꢀ3'ꢀyl)ꢀ
9,9ꢀdioctylfluorene (V). Compound IV (9.79 g,
14.45 mmol), 1,3ꢀdiphenylacetone (6.29 g, 29.9 mmol),
and 400 mL of ethyl alcohol were placed in a threeꢀ
neck flask (500 mL) equipped with a stirrer, a reflux
condenser, and a dropping funnel. The reaction mixꢀ
ture was heated to gentle boiling, a solution of potasꢀ
sium hydroxide (0.85 g in 11.5 mL of water) was
added, and the mixture was stirred for 2 h. The reacꢀ
tion mass was cooled. The resulting black precipitate
was filtered off, washed with distilled water and cold
alcohol, and crystallized from heptane. The yield of
of II (mp 52–54 C) was 46.0 g (91.2%).
°
2,7ꢀBis(phenylethynyl)ꢀ9,9ꢀdioctylfluorene (III).
Compound II (10.96 g, 20 mmol), phenylacetylene
(4.10 g, 40 mmol), 160 mL of triethylamine, pallaꢀ
dium catalyst (0.098 g, 0.13 mmol), triphenylphosꢀ
phine (0.10 g, 0.42 mmol), and copper(I) iodide
(0.088 g, 0.46 mmol) were placed in a threeꢀneck flask
equipped with a stirrer, a reflux condenser, and an
argon inlet tube. The reaction mixture was refluxed for
120 h. The resulting precipitate was filtered off. The
filtrate was evaporated. The residue was recrystallized
from hexane. The yield of III as light yellow crystals
black crystals of
(95.4%).
V
(mp 168–170 C) was 13.81 g
°
2,7ꢀBis(trimethylsilylethynyl)ꢀ9,9ꢀdioctylfluorene
(VI). Compound (12.38 g, 38.24 mmol), trimethylsꢀ
I
ilylacetylene (9.36 g, 95.40 mmol), 500 mL of triethylꢀ
amine, palladium catalyst (0.8 g, 1.08 mmol), tripheꢀ
nylphosphine (0.40, 1.53 mmol), and copper(I) iodide
(0.22 g, 1.16 mmol) were placed in a threeꢀneck flask
(mp 82–84 C) was 10.1 g (85.2%).
°
2,7ꢀBis(phenylglyoxalyl)ꢀ9,9ꢀdioctylfluorene (IV). (1 L) equipped with a stirrer, a reflux condenser, and
Compound III (10.05 g, 17 mmol), potassium perꢀ an argon inlet tube. The reaction mixture was refluxed
DOKLADY CHEMISTRY Vol. 432
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2010

164
KESHTOV et al.
for 12 h. Then, the resulting precipitate was filtered
All PSPFs were synthesized analogously. Some
off. The filtrate was evaporated on a rotary evaporator. characteristics of them are presented in Table 3.
The precipitate was crystallized from hexane. The
Polymer VIIIb. 1H NMR (CDCl3
, δ, ppm: 6.90–
yield of light yellow crystals of VI (mp 89–91 С) was
°
7.51 (m, 42H, arom.), 0.11–1.25 (m, 34H, aliph.).
20.97 g (94.05%).
Polymer VIIIc. 1H NMR (CDCl3
,
δ
, ppm: 6.65–
2,7ꢀBis(ethynyl)ꢀ9,9ꢀdioctylfluorene (VII). A porꢀ
tion of 245 mL of methanol and 22 mL of a 20% aqueꢀ
ous potassium hydroxide were added to a vigorously
stirred solution of compound VI (13.81 g, 23.69 mmol) in
440 mL of THF. The reaction mixture was stirred at
room temperature for 10 h. The solvent was removed,
and the residue was crystallized from hexane. The
7.54 (m, 48H, arom.), 0.10–1.52 (m, 34H, aliph.).
ACKNOWLEDGMENTS
This work was supported by the International Sciꢀ
ence and Technology Center (project no. 3718), the
Russian Academy of Sciences (under the aegis of the
program “Design of New Metallic, Ceramic, Glass,
Polymeric, and Composite Materials” of the Division
of Chemistry and Materials Science, RAS), and the
Presidium of the RAS (program no. P21 “Foundations
of Basic Research of Nanotechnologies and Nanomaꢀ
terials”).
yield of white crystals of VII (mp 44–46 C) was 8.54 g
°
(82.2%).
Synthesis of Polymers
Polymer VIIIa. Bis(cyclopentadienone)
V (1.0034 g,
1 mmol) and bis(ethynyl) VIIa (0.4387 g, 1 mmol)
were placed into a highꢀpressure stainless steel reactor
(with an inner volume of 22 mL) preliminarily purged
with carbon dioxide. A piston pump (High pressure
equipment) was used for supplying liquid carbon dioxꢀ
ide and creating a required pressure of 200 bar at room
temperature. The reactor was placed into a thermostat
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°
stirred for 10 h.
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vol. 19, pp. 4224–4228.
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and dried in a vacuum drying cabinet for 24 h at 80
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DOKLADY CHEMISTRY Vol. 432
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2010